http://caltechbook.library.caltech.edu"item available are small in quantity, but you don't need worried about copyright"

Textbook Revolution“TBR’s mission is to drive the adoption of free textbooks by teachers and professors. We want to get these books into classrooms. Our approach is to bring all of the free textbooks we can find together in one place, review them, and let the best rise to the top and find their way into the hands of students in classrooms around the world.”

Wikibooks“Wikibooks is a Wikimedia community for creating a free library of educational textbooks that anyone can edit. Wikibooks began on July 10, 2003, since then Wikibooks has grown to include over 30,398 pages in a multitude of textbooks created by volunteers like you!”

Open Text Book“Open Text Book is a registry of textbooks (and related materials) which are open — that is free for anyone to use, reuse and redistribute. It is run by the Open Knowledge Foundation”

Scribd“Through Scribd.com, iPaper, and the Scribd Platform, Scribd is changing the way people view, publish, and monetize documents. Through our vast library of content and our unique document display technology, we hope to unlock the information in the world’s documents and make it readily accessible to everyone.”Scribd doesn’t specifically aim to provide free textbooks but there seem to be many available. Searches for specific titles or subjects often bring back a substantial list of results. Outside of textbooks, Scribd can be used as a deep source of student contributed notes.Nearly all of the sites above are not in violation of any copyright laws. Scribd is the exception, but only because they allow users to upload materials. However, they seem responsive to DMCA take down notices.

TextbooktorrentOne of my fave is textbooktorrents. Textbook Torrents is using BitTorrent, a peer-to-peer file sharing protocol, to let students download textbooks for free. The site not only allows Torrents for those open textbooks but allows users to scan and upload other textbooks.The textbooktorrents.com website is currently offline. The error data (”not found on this server”) just confirmed that the owner took it down or that the host (DreamHost) took it down. Please note that Google still has pages from textbooktorrents.com in their index. Google hasn’t banned the site, it’s simply not ranking high because there’s no longer any relevant content on these pages.